The long-term objective of this research is to understand the cortical mechanisms that underlie spatial hearing. Although there is now a wealth of neurophysiological and psychophysical data related to sound localization mechanisms, the is a paucity of formal stistical and mathematical models that provide a theoretical framwork for this research, that might integrate these large knowledge bases, that give insight into the underlying mechanisms, or that drive new laboratory experimentation. The models will be based on, and provide a bridge between, the directional selectivity of primary auditory cortical neurons as measured in single-neuron electrophysiological experiments and human spatial acuity as determine in complementary psychophysical studies. The cortical data are in the form of spatial receptive fields measured with the aid of a virtual space paradigm. We propose to pursue four related specific aims: 1) We will functionally approximate the directional sensitivity of the auditory cortical neurons as measured by their response patterns using the von Mises basis function. This set of basis functions is unique in that it is spherical rather than Cartesian. This approach is similar to the framework developed to describve simple-cell receptive fields in visual cortex using Gabor functions or Difference-of-gaussians, 2) We will develop ideal observer models of spatial direction based on a theory of maximum-likelihood estimates, and test these models psychophysically. 3) We will develop models of maximum-likelihood estimators of latency reference to test the feasibility of latency based coding of sound direction. 4) We will develop ideal observer models based on correlated response patterns. This approach of integrating theoretical modeling with electrophysiological and psychophysical analyses will provide new insights into cortiucal mechanisms underlying spatial hearing and drive new physiological and behavioral studies.